Thermonuclear X-ray Bursts with late secondary peaks observed from 4U 1608-52

Abstract

We report the temporal and spectral analysis of three thermonuclear X-ray bursts from 4U 1608-52, observed by the Neutron Star Interior Composition Explorer (NICER) during and just after the outburst observed from the source in 2020. In two of the X-ray bursts, we detect secondary peaks, 30 and 18 seconds after the initial peaks. The secondary peaks show a fast rise exponential decay-like shape resembling a thermonuclear X-ray burst. Time-resolved X-ray spectral analysis reveals that the peak flux, blackbody temperature, and apparent emitting radius values of the initial peaks are in agreement with X-ray bursts previously observed from 4U 1608-52, while the same values for the secondary peaks tend toward the lower end of the distribution of bursts observed from this source. The third X-ray burst, which happened during much lower accretion rates did not show any evidence for a deviation from an exponential decay and was significantly brighter than the previous bursts. We present the properties of the secondary peaks and discuss the events within the framework of short recurrence time bursts or bursts with secondary peaks. We find that the current observations do not fit in standard scenarios and challenge our understanding of flame spreading.

Accepted for publication in the Astrophysical Journal

References in corpus (17)

• The NumPy array: a structure for efficient numerical computation
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The effect of accretion on the measurement of neutron star mass and radius in the low-mass X-ray binary 4U 1608-52
• Evidence for enhanced persistent emission during sub-Eddington thermonuclear bursts
• A model for the waveform behavior of accreting millisecond pulsars: Nearly aligned magnetic fields and moving emission regions
• Discovery of X-ray burst triplets in EXO 0748-676
• Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-Driven Convection
• Reaction Rate and Composition Dependence of the Stability of Thermonuclear Burning on Accreting Neutron Stars
• Rotational effects in thermonuclear Type I Bursts: equatorial crossing and directionality of flame spreading
• Signature of Temporary Burning Front Stalling from a Non-Photospheric Radius Expansion Double-peaked Burst
• Long tails on thermonuclear X-ray bursts from neutron stars: a signature of inward heating?
• The accretion rate dependence of burst oscillation amplitude
• Thermonuclear Flame Spreading on Rapidly Spinning Neutron Stars: Indications of the Coriolis Force?
• On the dependence of X-ray burst rate on accretion and spin rate
• The efficiency of nuclear burning during thermonuclear (Type I) bursts as a function of accretion rate
• The study of multi-peaked type-I X-ray bursts in the neutron-star low mass X-ray binary 4U 1636$-$536 with RXTE
• Multiple X-ray bursts and the model of a spreading layer of accreting matter over the neutron star surface

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